Dear Recyclebank: Why must metal cans be cleaned before recycling? Won’t any small bits of food remaining on the metal be burned off during the melting process? –Dan K.

Dear Dan: Many, but not all, materials can be easily cleaned during the recycling process. Depending on the recycling system your local waste handler uses, this may mean you need to do some quick cleaning before tossing that soup can in the recycle. Cleaning recyclables before putting them in your recycling is most important in areas where single-stream recycling systems are used. Dual-stream recycling systems, where paper products are kept separate from the rest, depend less on consumers cleaning every last bit of food off of metal cans, for instance.

If you’re required to separate your metal, plastic, and glass recyclables from your paper products, you have a dual-stream recycling system. In this case, while you’ll likely still be asked to do a certain amount of rinsing and cleaning before you place items in your recycling container, the need to clean is less pressing than in a single-stream system where all recyclables are collected together without any sorting on your end.

Why? It all boils down to cross-contamination. Paper will absorb grease and other food particles from other dirty recyclables it comes into contact with. Unlike metal, glass, or plastic, paper is typically processed at temperatures below the boiling point (212˚ Fahrenheit). In fact, anything above 250˚(F) can cause damage to the paper fibers being recycled. Because of this, the paper recycling process won’t burn off food residue in the way that other materials-recycling processes might. Contaminated paper can lower the quality of a batch of recycling, making it unsuitable for the market. This unusable material will usually be sent to the landfill once it arrives at the materials recovery facility (MRF) to prevent further contamination at the MRF: Recycling costs can go up accordingly, which can drive up the cost of recycled goods for consumers, which could then diminish the viability of the recycling system. That’s no good.

While single-stream recycling is more convenient for consumers, the perils of contamination can take their toll. The EPA reported that in 2014 an average of 16% (by weight) of incoming single-stream recycling is contaminated. Spread across the entire US, that figure adds up to a monumental loss in material value and resources. While there are multiple causes for this, including damaged items and the incorrect inclusion of non-recyclables in people’s recycling containers, if everyone made an effort to keep their cans and jars clean, it would make a positive dent in that number.

If your area uses dual-stream recycling, you probably don’t need to be as concerned. However, keep in mind that any cleaning you do will save time and labor on the other end, helping to drive down costs and keep your program profitable. Of course, always follow any cleaning guidelines laid out by your hauler.

SOURCES: Environmental Protection Agency, North Carolina State University